Topological Supramolecular Complexation of Metal-Organic Polyhedra for Tunable Interconnected Hierarchical Microporosity in Amorphous Form

Abstract

The precise engineering of microporosity is challenging due to the interference at the sub-nm scale from unexpected structural flexibility and molecular packing. Herein, the concept of topological supramolecular complexation is proposed for the feasible fabrication of hierarchical microporosity with broad tunability in amorphous form. The 2.5 nm metal-organic polyhedra (MOP) are complexed with quadridentate ligands through hydrogen and coordination bonding while the mismatch between the MOPs’ cuboctahedron and ligands’ tetrahedron topology leads to frustrated packing with extrinsic microporosity. Amorphous supramolecular frameworks can be obtained that integrate the intrinsic microporosity of the MOPs with the extrinsic porosity from the frustrated packing. The topologies, sizes and flexibility of ligands as well as ligand/MOP ratios are systemically varied, and the pore size distribution can be precisely adjusted. The hierarchical structures ranging from molecular packing to the morphologies of meso-scale assemblies are probed using ultra-small, small- and wide-angle X-ray scattering, enabling the quantitative evaluation of the micropores interconnectivity for the understanding of gas permeation performance. Gas separation membranes with permselectivity surpassing the Robeson upper bound can be designed. The findings not only give insight into the microscopic mechanism of supramolecular frustrated packing from topological design, but also pave new avenues for the cost-effective fabrications of microporous frameworks.